RMT general secretary Bob Crow said: “LU seem to be hell-bent on confrontation by unilaterally introducing new working practices which mean they can make people work what hours they like, when they like.”

Phil Hufton, LU’s chief maintenance officer, denied the union’s allegations, and said the decision to strike over rosters was “ludicrous”.

The dispute is about the introduction of rosters designed to ensure that planned engineering staff are always available. The staff affected work on the former Metronet sections of the Tube network – all lines except for the Northern, Piccadilly and Jubilee.